The present invention relates to a user input device and more particularly to a user input device having a membrane wherein deformation of the membrane may be measured and localized.
Various user input devices wherein a user inputs location information by applying pressure to a particular location on the device. If the device is an input to a computer system, the location of the user's application of pressure may be used to position a cursor on a display, for example. Other applications include computer-aided-drafting (CAD) and entry of handwritten text.
Such user input devices have various structures and theories of operation. For example, one device provides that a conductive sheet is superimposed over a resistive sheet. The resistive sheet has a voltage V.sub.1 at an upper edge and a voltage V.sub.2 at a lower edge. When the user applies pressure at a location on the resistive sheet, the corresponding location on the conductive sheet becomes connected to a voltage divider which provides a voltage between V.sub.1 and V.sub.2 having a magnitude dependent on location relative to the upper and lower edges. By measuring the voltage on the conductive sheet, the location of the applied pressure can be determined along an axis between the upper and lower edges. To find the location along the other axis, voltages V.sub.1 and V.sub.2 are applied to the left and right edges instead.
Various other devices detect the location and/or magnitude of user application of pressure by monitoring capacitance, inductance, voltage generated by a piezoelectric material etc. All of the prior art devices, however, share common shortcomings. The devices cannot detect simultaneous application of pressure to two or more locations. Furthermore, in measuring the amount of pressure applied, the devices provide poor dynamic range.